1. Field of the Invention
The present invention relates to a rolling element spacer which, in various rolling guide devices each having an endless circulation passage for balls such as a linear guide device and a ball screw device, is interposed between the mutually adjoining balls in the endless circulation passage and reduces frictions between the balls and a heat generation to thereby smoothen the rolling thereof.
2. Description of the Related Art
Hitherto, as a rolling guide device in which a pair of members continuously performing a relative motion through an endlessly circulating ball row, there have been known devices such as a linear guide device which is used in a linear guide portion in a machine tool, a carrying device and the like and which guides a movable body such as a table on a stationary portion such as a bed or a saddle, and a ball screw which is used together with this linear guide device and which gives a stroke of a linear motion corresponding to a rotation amount of a motor to the movable body.
The former linear guide device comprises a bearing rail which is disposed on the stationary portion and in which a rolling groove for the balls is formed along a longitudinal direction, and a sliding base which has a load rolling groove facing the rolling groove of the bearing rail through many balls and in which there is formed an endless circulation groove for the balls rolling on the load rolling groove, and it is constituted such that, in accompaniment with the endless circulation of the balls, the sliding base supporting the movable body continuously performs the linear motion along the bearing rail. Further, reversely to this, there is a case where it is constituted such that the bearing rail is moved relative to the fixed sliding base.
On the other hand, the latter ball screw comprises a screw shaft in which there is formed a spiral ball rolling groove with a predetermined lead, and a nut member which has a load rolling groove facing the ball rolling groove through many balls and in which there is formed an endless circulation passage for the balls rolling on the load rolling groove, and it is constituted such that, in accompaniment with a relative rotation motion between the screw shaft and the nut member, the balls circulate in the endless circulation passage, and the nut member and the screw shaft relatively move in an axial direction.
On the other hand, in such a rolling guide device, since the individual ball circulating in the endless circulation passage mutually contacts with the balls positioned before and after it, in case that it is used at a high speed, there have been such possibilities that, besides the fact that the balls are worn in relatively short time by a friction between the balls for instance, there arises a disadvantage such as the fact that the ball or the load rolling groove generates a seizure owing to a friction heat. Further, when reversing a motion direction, i.e., when reversing a circulation direction, an arrangement of the balls in the endless circulation passage is liable to be disturbed and, in an extreme case, there arises a so-called lock phenomenon in which the balls clog in the endless circulation passage, so that there has been a possibilities that the rolling guide device itself becomes impossible to operate. Therefore, as one for solving such drawbacks, in Japanese Patent Laid-Open No. 315835/1999 Gazette, there is disclosed a rolling guide device in which a rolling element spacer is interposed between the balls mutually adjoining in the endless circulation passage.
In the rolling guide device disclosed in the above Gazette, it is adapted such that a synthetic resin made rolling element spacer referred to as separator is arranged alternately with the ball in the endless circulation passage, thereby preventing the balls from mutually contacting. Such a separator is formed in a disk-like form whose outer diameter is smaller than a diameter of the ball and, in its both front/rear faces contacting with the balls, there are formed ball holding seats whose curvatures are larger than a curvature of a spherical face of the ball. By this, if the ball and the separator are alternately arranged without a gap in the endless circulation passage, each ball becomes a state of being sandwiched by a pair of separators adjoining before and after it, so that it circulates in the endless circulation passage together with the separators without disturbing a row even when reversing the circulation direction.
However, like the rolling element spacer shown in the Japanese Patent Laid-Open No. 315835/1999 Gazette, if the ball holding seat which sliding-contacts with the ball is formed in a concave curved face form whose curvature is larger than the spherical face of the ball, since a gap is formed between a peripheral edge portion of the ball holding seat and the ball, the ball rocks with respect to the rolling element spacer, so that there is a problem that it is impossible to completely eliminate a meander of the balls in the endless circulation passage.
On the other hand, from a viewpoint of preventing the meander of the balls in the endless circulation passage, it is necessary that the ball settles on the ball holding seat of the rolling element spacer without rocking, and therefor it is necessary that ball holding seat is formed in a concave spherical face form nearly approximating the spherical face of the ball. However, in case that the ball holding seat is formed in such a concave spherical face form, a contact area between the ball and the ball holding seat becomes large, so that there are possibilities of an increase in sliding contact resistance of the rolling element spacer with respect to the ball, a premature wear of the rolling element spacer, and the like.
Further, in case that the ball holding seat is designed such that its diameter is small in order to avoid the increase in sliding contact resistance with respect to the ball, there has been a disadvantage that the rolling element spacer falls out from between the mutually adjoining balls even if a slight gap is generated between the ball and the rolling element spacer.
The invention has been made in view of such a problem, and its object is to provide a rolling element spacer which makes a sitting of the ball with respect to the ball holding seat good to thereby intend to stabilize an alignment of the balls and the rolling element spacers in the endless circulation passage, can reduce the sliding contact resistance acting to the ball, and can effectively prevent the rolling element spacer from falling out from between the balls.
In order to achieve the above object, the invention provides a rolling element spacer used in a rolling guide device in which a pair of members perform a relative continuous motion through an endlessly circulating ball row, interposed between balls mutually adjoining in its endless circulation passage, and circulating together with the balls, characterized in that it has a pair of ball holding seats each of which is formed in a concave spherical face form nearly approximating a spherical face of the ball and sliding-contacts with the ball and, around each ball holding seat, there is formed an annular dropout prevention portion protruding in a ball arranging direction than an edge portion of the ball holding seat and kept in non-contact with respect to the ball seated on the ball holding seat.
According to such a technical means, since the ball folding seat with which the ball sliding-contacts is formed in the concave spherical face form nearly approximating the spherical face of the ball, a gap is scarcely formed between the spherical face of the ball and the ball holding seat, so that the siting of the ball with respect to the ball holding seat is stabilized. Therefore, in case that the rolling element spacers and the balls are alternately arranged in the endless circulation passage of the rolling guide device, it is intended to stabilize the alignment of the balls and the rolling element spacers, so that it become possible to prevent a meander of the balls in the endless circulation passage.
Further, since the annular dropout prevention portion kept in non-contact with respect to the ball is formed around the ball holding seat and the dropout prevention portion protrudes in the ball arranging direction than the edge portion of the ball holding seat, even if a gap is generated between the ball and the rolling element spacer and thus the rolling element spacer becomes likely to fall out from between the mutually adjoining balls, it becomes possible to prevent beforehand a dropout accident of the rolling element spacer by the fact that the dropout prevention portion engages with the ball. Accordingly, since a diameter of the ball holding seat can be determined irrespective of the dropout of the rolling element spacer and thus the ball holding seat can be formed in a size as minimum as necessary, it becomes possible to make a contact area between the ball holding seat and the ball small, thereby reducing the sliding contact resistance acting to the ball. Further, since the dropout prevention portion is kept in non-contact with respect to the ball under a state that the ball seats on the ball holding seat, there is no case that the sliding contact resistance acting to the ball increases, by the fact that the dropout prevention portion is provided.
In case that the ball holding seat is formed in the concave spherical face form nearly approximating the spherical face of the ball, since a peripheral edge portion of the ball holding seat contacts with the spherical face of the ball, a lubricant adhered on the ball is scraped by the peripheral edge portion, so that the ball is liable to come into a state of insufficient lubrication. However, according to the rolling element spacer of the invention, since the dropout prevention portion provided around the ball holding seat is kept in non-contact with the spherical face of the ball, the lubricant is liable to enter into the gap between the dropout prevention portion and the ball, so that a lubricating state of the ball can be maintained well even in case that the ball holding seat is formed in the concave spherical face form nearly approximating the spherical face of the ball. Accordingly, from a viewpoint of making a holding state of the lubricant in the rolling element spacer of the invention further good, it is preferable to form an annular groove between the ball holding seat and the dropout prevention portion surrounding it and utilize this annular groove as a lubricant sump. If constituted in this manner, since the lubricant flowing into the gap between the ball and the dropout prevention portion is stored in the annular groove, it becomes possible to always apply the lubricant to a surface of the ball.
On the other hand, in the endless circulation passage of the rolling guide device, since it is difficult to completely eliminate a gap between the ball and the rolling element spacer, it follows that the rolling element spacer and the ball are repeating collisions bit by bit during a circulation of the balls. Therefore, from a viewpoint of reducing a fatigue and decreasing a collision noise of the balls owing to such collisions, it is preferable that the ball holding seat with which the ball sliding-contacts is formed of a suitably soft material. In contrast to this, since the dropout prevention portion is one for preventing the rolling element spacer from falling out from between the mutually adjoining balls, it must not be easily deformed by being pushed by the ball in case that such a situation occurs, so that it is preferable that it is formed of a hard material. Accordingly, from such a viewpoint, it is preferable that the ball holding seat and the dropout prevention portion provided in the rolling element spacer of the invention are molded respectively by different resin materials, and the dropout prevention portion is molded by the resin material harder than the ball holding seat.
Incidentally, the dropout prevention portion may be formed in a continuous annular form, but the dropout prevention portion may be made by providing a protrusion separated by a slit in the annular form.
As explained above, according to the rolling element spacer of the invention, since each of a pair of ball holding seats with which the balls sliding-contact is formed in the concave spherical face form nearly approximating the spherical face of the ball and, around each ball holding seat, there is formed the annular dropout prevention portion protruding in the ball arranging direction than the edge portion of the ball holding seat and kept in non-contact with respect to the ball seated on the ball holding seat, it is possible to intend to stabilize the alignment of the balls and the rolling element spacers in the endless circulation passage while making the sitting of the ball with respect to the ball holding seat good and intend to decrease the sliding contact resistance acting to the ball, and additionally it becomes possible to effectively prevent the rolling element spacer from falling out from between the balls.